Mac IE5's rendering is the best since it not only does full
alpha-transparency but also gamma and color correction. See the
PNG-Supporting Browsers page for details.

This set is provided courtesy of Stefan Schneider.
If the two images on the right are transparent but the one
on the left has a black background, the browser was probably compiled with a
buggy version of libpng. The bug is fixed in libpng 0.96 and later,
and a trivial patch is available (for
browser implementors, that is) for earlier versions of libpng.

The image on the right is a full 32-bit RGBA image (that is, truecolor with
a full alpha channel). The two on the left are 8-bit palette images with
full transparency chunks--in other words, their palettes are effectively
RGBA values instead of the normal RGB. The one on the left has a 256-entry
palette, while the one in the center has 255 entries; both were created with
Stefan's LatinByrd application.

As a nice demonstration of the power of the palette-alpha images, here's a
composite JPEG image of the toucan on top of his twin, provided by
Glenn Randers-Pehrson. Note how
the shadow of the toucan in front falls across his buddy:

The following set is provided by Greg's colleague, Pieter van der Meulen.
All of these images are interlaced, have transparency, and should be
rendered with the same green background as the page. If the images have
obvious rectangular borders (due to the color specified in the bKGD chunk),
the browser is broken. (The images should use their respective bKGD
colors when viewed in a stand-alone image viewer with no default background
of its own, however.)

These images are quarter-scale, interlaced, RGBA-palette (8-bit) versions
of the original 32-bit RGBA images; each is between 35k and 70k. Click on
any of them to bring up a page with the corresponding half-scale version of the
image (also 8-bit), which in turn is linked to the full-size, 32-bit version.
The conversion to 8-bit palette mode was accomplished by means of
modified versions of
some of the NetPBM tools.